Quick answer
Your BMR, or basal metabolic rate, is the energy your body uses at complete rest. This calculator estimates it with the Mifflin-St Jeor equation, which a systematic review found came within 10 percent of measured resting energy for more people than other common equations. At a resting figure of 1,500 calories, 10 percent is 150 calories.1,2
Estimate your resting energy
Enter your age, height and weight to see an estimate.
These are estimates from a published equation, not advice for you. They can be off by hundreds of calories for an individual. Ask your doctor first if you are pregnant or nursing, under 19, have a medical condition, or have ever had a difficult relationship with food.
Key facts
- The formula is 10 times weight in kilograms, plus 6.25 times height in centimeters, minus 5 times age in years, then plus 5 for men or minus 161 for women.2
- BMR is measured at complete rest, usually after sleep and 12 or more hours without food. Resting metabolic rate is measured awake and runs about 10% higher.3
- Mifflin and colleagues measured 498 adults aged 19 to 78 and found that the 1919 Harris-Benedict equations overestimated their resting energy by 5%.2
- Fat-free mass explains 60 to 80 percent of the differences in resting energy between people and body weight alone about 50 percent, so two people with identical inputs can still differ.3
- Resting energy is the largest part of the day's total, typically 60 to 70 percent, but it leaves out digestion and activity.3
BMR or resting metabolic rate: what is the difference?
Basal metabolic rate is the energy your body needs at complete physical, mental and digestive rest. It is usually measured after sleep, before getting out of bed, 12 or more hours after the last meal. Resting metabolic rate is measured awake, lying down, with no food or exercise in the previous 4 to 5 hours, and it runs about 10 percent higher than the basal figure.3
Mifflin's team measured the second kind, resting energy expenditure, so strictly the equation estimates resting energy rather than the basal minimum. Most calculators call the result BMR anyway, and so does this one. The calculator shows a single figure, resting calories a day. It does not ask about activity or goals, which makes it the starting point for the TDEE calculator and not a calorie target in itself.2,3
The Mifflin-St Jeor formula, term by term
| Part | Men | Women |
|---|---|---|
| Weight | 10 calories for each kilogram | 10 calories for each kilogram |
| Height | 6.25 calories for each centimeter | 6.25 calories for each centimeter |
| Age | 5 calories fewer for each year | 5 calories fewer for each year |
| Fixed amount | Plus 5 | Minus 161 |
Here is the arithmetic for a 35-year-old woman who is 165 centimeters tall and weighs 65 kilograms. Weight contributes 650 calories and height 1,031.25. Age takes off 175 and the women's constant takes off 161. The total is 1,345.25, shown as 1,345 calories a day.2
In the original paper the sexes share one equation with a 166 calorie term for men. The authors reported that the simplified separate formulas, which are the ones used here, predicted just as well. Pounds are divided by 2.2046 and inches multiplied by 2.54 before the formula runs, and nothing you enter leaves your browser.2
BMR calculator for women and men: six sizes compared
| Person | Age | Height | Weight | Resting calories |
|---|---|---|---|---|
| Woman | 25 | 160 cm | 55 kg | 1,264 |
| Woman | 35 | 165 cm | 65 kg | 1,345 |
| Woman | 55 | 168 cm | 75 kg | 1,364 |
| Man | 25 | 175 cm | 70 kg | 1,674 |
| Man | 35 | 180 cm | 80 kg | 1,755 |
| Man | 55 | 178 cm | 90 kg | 1,743 |
Two patterns show in the table. Each kilogram of weight adds 10 calories and each year of age takes off 5, so the older woman, who is heavier and a little taller, comes out slightly above the younger one, while the older man, who is heavier but a little shorter, lands slightly below the younger man. The sex term is a fixed 166 calories between men and women at the same size and age.2
The National Academies' review found that sex had little effect on resting energy once body mass and composition were accounted for, even though the equation keeps a sex term. The ISSN also notes how little research exists on women and older people, and the systematic review of equations says older adults were underrepresented in the studies, so a result for either group deserves extra caution.1,3,4
What makes resting energy higher or lower?
The formula has four inputs, and the body has more going on. The National Academies list age, sex, body size and composition, and genetics as influences. Body composition counts most: fat-free mass, which includes muscle, connective tissue, water and bone, uses about 20 calories per kilogram a day against about 5 for fat tissue, and it explains 60 to 80 percent of the differences between people.3
Two adults with the same sex, age, height and weight get the same answer from this calculator, even if one carries more muscle. That is a built-in limit of the four inputs.
Age works through body composition too. Basal energy measured in 2,008 people across 29 countries, once adjusted for body size, stayed stable from about 20 to 60 and then declined in older adults, which the National Academies say appears related to losses of fat-free mass and a decline in organ metabolism. The equation's age term is a single straight line across all of 19 to 78, so it cannot show that pattern.3
Eating less changes resting energy as well. The National Academies note that periods of underfeeding typically bring compensatory metabolic responses and losses of fat-free mass, which generally lower energy expenditure.3
How accurate is a BMR calculator?
In the 498 people Mifflin's team measured, weight, height, age and sex together explained about 71 percent of the variation in resting energy. Fat-free mass alone explained 64 percent, and weight alone 56 percent. That leaves roughly 29 percent of the variation unexplained, which is why a prediction for one person can be off.2
A systematic review compared the four equations most used in practice: Harris-Benedict, Mifflin-St Jeor, Owen, and the World Health Organization, FAO and United Nations University equation. Mifflin-St Jeor was the most reliable, with the most people predicted within 10 percent of measured and the narrowest error range. The panel still reported noteworthy errors for individuals and advised clinical judgment about when to accept an estimate.1
The only way to remove the estimation error is to measure resting energy with indirect calorimetry, which the same review suggests may help when an estimate fails an individual in a way that matters. The older Harris-Benedict equations from 1919 overestimated measured resting energy by 5 percent in Mifflin's group.1,2
Is BMR the number of calories to eat?
No. BMR leaves out the energy spent digesting food, about 10 percent of the day's total, and the energy spent on activity, which is the most variable part. Resting energy alone typically makes up 60 to 70 percent of what a person uses in a day.3
The calorie and macro calculators on this site stop a goal from falling below the resting estimate. That is a rule built into the tools, not a published safe limit, and it does not make eating at that number right for you. Talk to your doctor or a registered dietitian about intake targets.
Who should not rely on a BMR estimate alone
This calculator estimates resting energy for healthy adults. It is information, not advice for you, and for some people the estimate misses by more than 10 percent, which is 150 calories or more at a resting figure of 1,500. Ask your doctor first if any of these apply.1
- You are under 19. The people Mifflin's team measured were 19 to 78, and children and teens need separate equations.2,5
- You are pregnant or nursing. The National Academies report that resting and total energy expenditure both rise over the course of pregnancy, and this calculator does not account for that.3
- You live with an illness or take medicines that affect your weight or appetite. The equation was derived in healthy individuals and may not describe you.2
- You have a history of an eating disorder. NIMH calls eating disorders serious and says they can be treated successfully. A resting calorie figure should not be used to plan restriction without medical guidance.6
- You are older than 78, or you are shorter than 120 centimeters, taller than 230 centimeters, lighter than 35 kilograms or heavier than 250 kilograms. The calculator will not give a figure outside those limits.2
Questions people ask
What is a basal metabolic rate calculator?
It is a tool that estimates the energy your body uses at complete rest from your sex, age, height and weight. This one uses the Mifflin-St Jeor equation, which was built from resting energy measured in 498 healthy adults.2,3
Is there a BMR calculator for women?
Yes. Choose female and the equation ends in minus 161, where the male version ends in plus 5. The National Academies found sex mattered little once body composition was matched, and the ISSN notes that research on women is scarce.2,3,4
Is a resting metabolic rate calculator the same as a BMR calculator?
Nearly. Resting metabolic rate is measured awake and runs about 10 percent above BMR, and Mifflin's equation was fitted to resting measurements. Most calculators label the result BMR regardless.2,3
How accurate is a BMR calculator?
For many people it lands within 10 percent of measured resting energy. In a systematic review Mifflin-St Jeor did that for more people than any other common equation, but errors for individuals were still noteworthy.1
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Sources
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789. Opened 2026-10-11.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. Opened 2026-10-11.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Chapter 4, Factors Affecting Energy Expenditure and Requirements. Washington, DC: The National Academies Press; 2023. Opened 2026-10-11.
- Aragon AA, Schoenfeld BJ, Wildman R, et al. International society of sports nutrition position stand: diets and body composition. J Int Soc Sports Nutr. 2017;14:16. Opened 2026-10-11.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Summary. Washington, DC: The National Academies Press; 2023. Opened 2026-10-11.
- National Institute of Mental Health. Eating Disorders. National Institutes of Health. Last reviewed December 2024. Opened 2026-10-11.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.